Medical image processing apparatus, x-ray diagnostic apparatus, medical image processing method and x-ray diagnostic method

ABSTRACT

According to one embodiment, a medical image processing apparatus includes processing circuitry. The processing circuitry is configured to obtain time changes of concentrations of a contrast agent, based on at least X-ray contrast image data; generate a gray scale or a color scale by assigning a change in pixel value for at least one period, to a period shorter than a period from an initial time to an ending time of the time changes of the concentrations of the contrast agent; and generate blood vessel image data according to the gray scale or the color scale. The blood vessel image data have pixel values corresponding to times at which the concentrations of the contrast agent become a specific condition.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a continuation of Application PCT/JP2014/58369, filed on Mar.25, 2014.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2013-076471 filed on Apr. 1, 2013; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a medical imageprocessing apparatus, an X-ray diagnostic apparatus, a medical imageprocessing method and an X-ray diagnostic method.

BACKGROUND

DSA (Digital Subtraction Angiography) is known as one of imaging methodsfor blood vessels in an X-ray diagnostic apparatus. DSA is thetechnology to generate subtraction image data between frames of X-rayimage data before and after injecting a contrast agent into an object,for diagnosis. That is, X-ray image data are acquired before injecting acontrast agent as a mask image data for generating subtraction imagedata. On the other hand, X-ray contrast image data is acquired byinjecting the contrast agent. Then, DSA image data is generated fordiagnosis by subtraction processing between the X-ray contrast imagedata and the mask image data.

Such DSA image data can be generated as image data in which unnecessaryanatomies in observation of a blood vessel are removed. That is,diagnostic image data in which blood vessels enhanced by a contrastagent are depicted selectively can be obtained. Consequently, imagesuseful for diagnosis of a blood vessel can be displayed.

PRIOR TECHNICAL LITERATURE

[Patent literature 1] U.S. Pat. No. 8,050,474 B2

Even in the case of acquiring DSA images which are typical as bloodvessel images acquired by an X-ray diagnostic apparatus, precise bloodvessel structures for a diagnosis may not be determined when a cerebralarteriovenous malformation, a dural arteriovenous fistula or the like isdiagnosed. Specifically, it is often difficult to specify anddistinguish blood vessels through which a contrast agent flows into adiseased part.

Thus, an object of the present invention is to provide a medical imageprocessing apparatus, an X-ray diagnostic apparatus, a medical imageprocessing method and an X-ray diagnostic method which can obtainprecise blood vessel structures allowing blood vessels, through which acontrast agent flows into a diseased part, to be identified moreclearly.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a configuration diagram of an X-ray diagnostic apparatus and amedical image processing apparatus according to an embodiment of thepresent invention;

FIG. 2 shows a graph for explaining a method of identifying an inflowtime or an arrival time of a contrast agent to a blood vessel based on aconcentration profile of the contrast agent;

FIG. 3 shows the first example of color scale assigned to time phasescorresponding to the maximum values of concentration profiles of acontrast agent;

FIG. 4 shows an example of color scheme in the color scale shown in (C)of FIG. 3;

FIG. 5 shows the second example of color scale assigned to time phasescorresponding to the maximum values of concentration profiles of acontrast agent;

FIG. 6 shows an example of color scheme in the color scale shown in (C)of FIG. 5;

FIG. 7 shows an example of color scales generated for dynamicallychanging the color scale shown in (C) of FIG. 3;

FIG. 8 shows an example of color scales generated for dynamicallychanging the color scale shown in (C) of FIG. 5;

FIG. 9 shows an example of parametric image generated in the parametricimage generation part shown in FIG. 1; and

FIG. 10 is a flow chart which shows an operation of the X-ray diagnosticapparatus 1 shown in FIG. 1 and processing in the medical imageprocessing apparatus 12 shown in FIG. 1.

DETAILED DESCRIPTION

In general, according to one embodiment, a medical image processingapparatus includes processing circuitry. The processing circuitry isconfigured to obtain time changes of concentrations of a contrast agent,based on at least X-ray contrast image data; generate a gray scale or acolor scale by assigning a change in pixel value for at least oneperiod, to a period shorter than a period from an initial time to anending time of the time changes of the concentrations of the contrastagent; and generate blood vessel image data according to the gray scaleor the color scale. The blood vessel image data have pixel valuescorresponding to times at which the concentrations of the contrast agentbecome a specific condition.

Further, according to one embodiment, a medical image processingapparatus includes processing circuitry. The processing circuitry isconfigured to obtain time changes in pixel value corresponding to ablood vessel, based on blood vessel image data acquired by an imagediagnostic apparatus; generate a gray scale or a color scale byassigning a change in pixel value for at least one period, to a periodshorter than a period from an initial time to an ending time of the timechanges in the pixel value corresponding to the blood vessel; andgenerate blood vessel image data according to the gray scale or thecolor scale. The blood vessel image data have pixel values correspondingto times at which pixel values corresponding to the blood vessel becomea specific condition.

Further, according to one embodiment, an X-ray diagnostic apparatusincludes an X-ray tube, an X-ray detector and processing circuitry. TheX-ray tube and the X-ray detector acquire at least X-ray contrast imagedata from an object. The processing circuitry is configured to obtaintime changes of concentrations of a contrast agent, based on the atleast X-ray contrast image data; generate a gray scale or a color scaleby assigning a change in pixel value for at least one period, to aperiod shorter than a period from an initial time to an ending time ofthe time changes of the concentrations of the contrast agent; andgenerate blood vessel image data according to the gray scale or thecolor scale. The blood vessel image data have pixel values correspondingto times at which the concentrations of the contrast agent become aspecific condition.

Further, according to one embodiment, a medical image processing methodincludes: obtaining time changes of concentrations of a contrast agent,based on at least X-ray contrast image data; generating a gray scale ora color scale by assigning a change in pixel value for at least oneperiod, to a period shorter than a period from an initial time to anending time of the time changes of the concentrations of the contrastagent; and generating blood vessel image data according to the grayscale or the color scale. The blood vessel image data have pixel valuescorresponding to times at which the concentrations of the contrast agentbecome a specific condition.

Further, according to one embodiment, an X-ray diagnostic methodincludes: acquiring at least X-ray contrast image data from an object;obtaining time changes of concentrations of a contrast agent, based onthe at least X-ray contrast image data; generating a gray scale or acolor scale by assigning a change in pixel value for at least oneperiod, to a period shorter than a period from an initial time to anending time of the time changes of the concentrations of the contrastagent; and generating blood vessel image data according to the grayscale or the color scale. The blood vessel image data have pixel valuescorresponding to times at which the concentrations of the contrast agentbecome a specific condition.

A medical image processing apparatus, an X-ray diagnostic apparatus, amedical image processing method and an X-ray diagnostic method accordingto embodiments of the present invention will be described with referenceto the accompanying drawings.

FIG. 1 is a configuration diagram of an X-ray diagnostic apparatus and amedical image processing apparatus according to an embodiment of thepresent invention.

An X-ray diagnostic apparatus 1 includes an imaging system 2, a controlsystem 3, a data processing system 4 and a console 5. The imaging system2 has an X-ray tube 6, an X-ray detector 7, a C-shaped arm 8, a base 9and a bed 10. In addition, the data processing system 4 has an A/D(analog to digital) converter 11, a medical image processing apparatus12, a D/A (digital to analog) converter 13, and a display 14. Note that,the A/D converter 11 may be integrated with the X-ray detector 7.

The X-ray tube 6 and the X-ray detector 7 are settled at both ends ofthe C-shaped arm 8 so as to be mutually opposed at both sides of theinterjacent bed 10. The C-shaped arm 8 is supported by the base 9. Thebase 9 has a motor 9A and a rotation mechanism 9B. The motor 9A and therotation mechanism 9B drive so as to rotate the X-ray tube 6 and theX-ray detector 7 fast into a desired position together with the C-shapedarm 8 like a propeller.

As the X-ray detector 7, a FPD (flat panel detector) or I.I.-TV (imageintensifier TV) can be used. Furthermore, the output side of the X-raydetector 7 is connected with the A/D converter 11 of the data processingsystem 4.

The control system 3 drives and controls the imaging system 2 byoutputting control signals to the respective elements consisting of theimaging system 2. The control system 3 is connected with the console 5as an input circuit. Therefore, instruction of imaging conditions andthe like to the control system 3 can be input from the console 5.

Then, the imaging system 2 is configured to expose X-rays toward anobject O set on the bed 10 at mutually different angles sequentiallyfrom the rotatable X-ray tube 6 under control by the control system 3.In addition, the imaging system 2 is configured to acquire X-raystransmitting the object O from the plural directions sequentially asX-ray projection data by the X-ray detector 7. The X-ray projection dataacquired by the X-ray detector 7 are output to the A/D converter 11 asX-ray image data.

Furthermore, a contrast agent injector 15 is provided in the vicinity ofthe object O set on the bed 10 in order to inject a contrast agent intothe object O. Thus, X-ray contrast imaging of an object O can beperformed by injecting a contrast agent from the contrast agent injector15 into the object O. The contrast agent injector 15 can be alsocontrolled by the control system 3.

Next, configurations and functions of the medical image processingapparatus 12 will be described.

The input side of the medical image processing apparatus 12 is connectedwith the output side of the A/D converter 11. Meanwhile, the display 14is connected to the output side of the medical image processingapparatus 12 through the D/A converter 13. Moreover, the medical imageprocessing apparatus 12 is connected with the console 5. Then, directioninformation required for data processing can be input into the medicalimage processing apparatus 12 by operation of the console 5.

Note that, aside from the medical image processing apparatus 12 built inthe X-ray diagnostic apparatus 1 as illustrated in FIG. 1, a similarmedical image processing apparatus as an independent system may beconnected with the X-ray diagnostic apparatus 1 through a network.

The medical image processing apparatus 12 includes an image memory 16, asubtraction part 17, a filtering part 18, an affine transformation part19, a gradation conversion part 20, and a parametric image generationpart 21. The parametric image generation part 21 has a time phasespecifying part 22, a color coding part 23, and a color scale adjustmentpart 24.

The medical image processing apparatus 12 having such functions can beconfigured by a computer reading a medical image processing program.That is, processing circuitry may be used to configure the medical imageprocessing apparatus 12.

The image memory 16 is a storage circuit for storing X-ray image dataacquired by the imaging system 2. Therefore, when non-contrast X-rayimaging has been performed, non-contrast X-ray image data is stored inthe image memory 16. Meanwhile, when X-ray imaging has been performedwith injecting a contrast agent into an object O, X-ray contrast imagedata is stored in the image memory 16.

The subtraction part 17 has a function to generate time series DSA imagedata, depicting contrast-enhanced blood vessels, by subtractionprocessing between non-contrast X-ray image data read from the imagememory 16 and time series X-ray contrast image data.

The filtering part 18 has a function to perform desired filterprocessing, such as a high-pass filtering, a low-pass filtering, or asmoothing filtering, of arbitrary data.

The affine transformation part 19 has a function to perform affinetransformation processing, such as a scaling, a rotation movement, and aparallel translation, of X-ray image data, according to directioninformation input from the console 5.

The gradation conversion part 20 has a function to perform gradationconversion of X-ray image data by referring to an LUT (Look Up Table).

The parametric image generation part 21 has a function to acquire timechanges in concentration of a contrast agent based on time series DSAimage data or time series X-ray contrast image data and a function togenerate parametric image data, having pixel values corresponding totimes at which the concentrations of the contrast agent become aspecific condition, as blood vessel image data.

For that purpose, the time phase specifying part 22 has a function tospecify time phases, at which concentrations of the contrast agentbecome a specific condition, based on profiles indicating time changesin the concentrations of the contrast agent. Moreover, the color codingpart 23 has a function to assign colors corresponding to time phasesspecified by the time phase specifying part 22. The color scaleadjustment part 24 has a function to determine a color scale used forcolor coding in the color coding part 23.

The specific condition for assigning colors can be determined, accordingto diagnostic purposes, to concentrations of a contrast agentcorresponding to time points when the contrast agent has flowed in orarrived at a focused blood vessel, concentrations of a contrast agentcorresponding to time points when the contrast agent has flowed out froma focused blood vessel contrarily, or the like. For example, a timedefining the specific condition can be a time when a concentration of acontrast agent becomes the maximum value, a predetermined ratio of themaximum value, or a threshold value.

FIG. 2 shows a graph for explaining a method of identifying an inflowtime or an arrival time of a contrast agent to a blood vessel based on aconcentration profile of the contrast agent.

In FIG. 2, the horizontal axis shows the time phase direction while thevertical axis shows intensities of image signals, of DSA image data orcontrast image data, representing concentrations of a contrast agent. Asshown in FIG. 2, a profile in concentration change of the contrast agentcan be obtained as a curve, showing signal intensities changing in time,by focusing a pixel corresponding to a blood vessel region of the timeseries DSA image data or contrast image data.

A typical concentration change profile becomes a curve of which thevalue increases gradually with the inflow of a contrast agent anddecreases gradually with the outflow of the contrast agent. Therefore,when a threshold value TH for detecting a rising up of the curve is setfor values of the concentration change profile, it becomes possible toidentify a time phase at a start of contrast agent inflow into a focusedblood vessel as a time phase Tth when the concentration of the contrastagent has reached the threshold value TH.

However, in a case that noises are large, the time phase at the start ofa contrast agent inflow may be identified incorrectly. For this reason,a predetermined ratio within the range of 5% to 10% of the maximum valuein a concentration profile of a contrast agent may be used for thethreshold value so that influences of noises can be suppressed.Alternatively, a time phase Tmax at which a concentration of a contrastagent has reached the maximum value MAX or a time phase T_(max/2) atwhich a concentration of a contrast agent has reached 50% of the maximumvalue MAX may be detected, from a concentration profile, as a time phasewhen the contrast agent has arrived at a blood vessel, as shown in FIG.2. Hereinafter, an example case that an arrival time phase of a contrastagent is identified will be mainly described.

When the specification of a time phase, based on a concentration profileof a contrast agent, as shown in FIG. 2, is performed to each requiredpixel, and colors according to the specified time phases are assigned,parametric image data in which each blood vessel has been depicted incolors according to arrival times of the contrast agent or the like canbe generated.

Note that, a time change in concentration of a contrast agent at eachpixel representative of several pixels may be obtained by runningaverage processing. That is, a matrix size of image data whoseconcentration changes of a contrast agent should be obtained can beminified with smoothing processing. Moreover, concentration changes of acontrast agent may be obtained based on image data whose noises havebeen removed by low-pass filter processing. These processing also can besaid as running average processing or low-pass filtering processing ofconcentration profiles of a contrast agent in a spatial direction.

The running average processing or the low-pass filtering processing canalso be performed not only in spatial directions but also in a timedirection. In the case that the running average processing or thelow-pass filtering processing is performed in the time direction, theprocessing is performed to concentration profiles of a contrast agent inthe time direction.

Therefore, parametric image data can be generated based on time changesin concentration of a contrast agent after noise suppression processingin at least one of the time direction and spatial directions. Moreover,parametric image data can be generated based on time changes inconcentration of a contrast agent after low-pass filtering processing inat least one of the time direction and spatial directions. Thereby,smooth parametric image data from which the noises have beendramatically suppressed can be generated.

Moreover, parametric image data can also be generated based on timechanges, in concentration of a contrast agent, each having a datainterval shorter than a sampling interval of the concentrations of thecontrast agent corresponding to an imaging interval of X-ray contrastimage data. A time change, in a concentration of a contrast agent, whichhas a data interval shorter than a sampling interval of theconcentration of the contrast agent, can be obtained by arbitraryprocessing, such as interpolation processing, curve fitting processingusing a specific function, or gravity center calculation processing.Thereby, it becomes possible to identify an arrival time of a contrastagent or the like at each pixel with a higher precision. In particular,it is more effective in a case that at least one of running averageprocessing and low-pass filtering processing is performed.

FIG. 3 shows the first example of color scale assigned to time phasescorresponding to the maximum values of concentration profiles of acontrast agent.

(A) of FIG. 3 shows concentration profiles of a contrast agent at twodimensional positions (xi, yj) (i=1, 2, 3, . . . , m; j=1, 2, 3, . . . ,n) and arrival time phases Tmax (xi, yj) of the contrast agent specifiedbased on the maximum values MAXs of the concentration profiles. Thecontrast agent arrives at a position, which is close to an injectionposition of the contrast agent, relatively early. Therefore, specifiedtime phases are also relatively early. On the other hand, the contrastagent arrives at a position, which is away from the injection positionof the contrast agent, relatively late. Therefore, specified time phasesare also relatively late.

(B) of FIG. 3 shows an example of color scale assigned to the specifiedtime phases as shown in (A) of FIG. 3. As shown in (B) of FIG. 3, acolor scale can be generated by assigning a change in color pixel valuefor one period, consisting of R value, B value and G value, to a periodTall from the initial time to the ending time of time changes inconcentrations of a contrast agent obtained as the concentrationprofiles. That is, a color scale can be generated by assigning acontinuous color phase change for one period to the period Tall from theinitial time to the ending time of time change in concentration of acontrast agent.

According to the color scale as shown in (B) of FIG. 3, a twodimensional time phase map showing arrival time phases of a contrastagent can be color coded. Then, parametric image data in which bloodvessels have been depicted by different colors according to arrival timephases of a contrast agent can be generated.

However, when a difference in the arrival time phases Tmax (xi, yj) of acontrast agent between the pixel positions (xi, yj) is small relativelyto a range of the color scale, as shown in (A) of FIG. 3, a differencein color between the pixel positions (xi, yj) becomes also small.Therefore, it may become difficult to distinguish small difference oftime by the difference in color.

In particular, when X-ray imaging is performed for the purpose ofdiagnosing a dural arteriovenous fistula or a cerebral arteriovenousmalformation, it is important to observe blood flows between arteriesand veins. Therefore, it is often necessary to distinguish blood vesselshaving small differences in arrival times of a contrast agent.

Thus, a color scale can be changed in the color scale adjustment part 24so that even blood vessels between which differences in arrival times ofa contrast agent are small can be distinguished as differences in color.(C) of FIG. 3 shows an example of generating a color scale by assigningthe continuous color phase change for one period multiple times to theperiod Tall, from the initial time to the ending time of time changes inconcentrations of a contrast agent, as changes in pixel values. That is,a color scale in which a continuous color phase change is repeatedperiodically can be generated.

Such a color scale generated as described above can assign a change inpixel value, longer than the change in pixel value for one period, tothe period Tall from the initial time to the ending time of time changesin concentrations of a contrast agent. Note that, although the exampleof generating a color scale by assigning the change in pixel value forone period multiple times has been shown in (C) of FIG. 3, a color scalein which the whole change in pixel value is not an integral multiple ofthe change in pixel value for one period may also be generated.

The color scale as shown in (C) of FIG. 3 can be generated bydesignating a pixel value corresponding to the initial time phase ofconcentration profiles, a period Tscale of a change in pixel value, andthe initial pixel value in the period Tscale, with an operation of theconsole 5. Thereby, it is possible to generate a color scale in whichthe change in pixel value for one period is repeated according to thedesignated initial pixel value and the designated period Tscale. Then,the colors can be arranged in each period Tscale similarly to the colorscheme as shown in (B) of FIG. 3. Specifically, a color scale in which acolor phase showing the maximum value changes among red, green and bluein one period Tscale can be generated.

FIG. 4 shows an example of color scheme in the color scale shown in (C)of FIG. 3.

The three orthogonal axes in FIG. 4 represent R values, G values, and Bvalues, respectively. The R value, G value, and B value corresponding toeach time phase in the period Tscale can be determined along the sidesof the color triangle, whose vertexes are the maximum value of the Rvalues, the maximum value of the G values, and the maximum value of theB values, as shown in FIG. 4. Specifically, the colors can be arrangedso that the G value and the B value become zero and the R value becomesthe maximum value when the relative time is zero or Tscale, the R valueand the B value become zero and the G value becomes the maximum valuewhen the relative time is Tscale/3, and the R value and the G valuebecome zero and the B value becomes the maximum value when the relativetime is 2Tscale/3.

When such a color scheme is performed, parametric image data can begenerated so that the color changes from red to blue through green, andthen returns to red again according to the time phase. Note that, thecolors between red, green, and blue can be assigned to time phases sothat the R value, the G value, and the B value change linearly, forexample. Alternatively, the R values, the G values, and the B values mayalso be assigned to time phases so that the angle of a line segment,which connects the center of the color triangle with a point on thesides, changes linearly.

When parametric image data are generated according to a color scalegenerated by such a color scheme, blood vessels can be distinguished asa difference in colors even when differences in arrival times of acontrast agent are small. That is, arrival times of a contrast agent canbe understood in detail.

Note that, the most visible color is red. Therefore, as exemplified inFIG. 4, setting the color of an initial time phase, which corresponds tothe earliest arrival time of a contrast agent, to red leads to animprovement of visibility. That is, it is effective to set a colorvalue, corresponding to the initial time phase of a color scale, to themaximum value of the R value. Moreover, as another example, it is alsouseful to adjust the initial time phase so that a focused time phasebecomes red.

FIG. 5 shows the second example of color scale assigned to time phasescorresponding to the maximum values of concentration profiles of acontrast agent.

(A) of FIG. 5 shows concentration profiles of a contrast agent at twodimensional positions (xi, yj) (i=1, 2, 3, . . . , m; j=1, 2, 3, . . . ,n) and arrival time phases Tmax (xi, yj) of the contrast agent specifiedbased on the maximum values MAXs of the concentration profiles,similarly to (A) of FIG. 3.

Then, the color scale as shown in (B) of FIG. 5, in which a change incolor pixel value is assigned to the period Tall from the initial timeto the ending time of time changes in concentrations of a contrastagent, can be changed into the color scale shown in (C) of FIG. 5. Thecolor scale shown in (C) of FIG. 5 is generated by assigning thecontinuous color phase change for one period, as a change in pixelvalue, to a designated period. The period to which the change in pixelvalue is assigned can be determined by designating a starting time phaseT1 and an ending time phase T2. The starting time phase T1 and theending time phase T2 can be designated by selecting corresponding imagesrespectively from time series X-ray contrast images or time series DSAimages.

Note that, a color scale can also be generated by assigning a change inpixel value, such as a change in pixel value for multiple periods asshown in (C) of FIG. 3, longer than one period, to the designated periodas shown in (C) of FIG. 5. That is, a color scale can be generated byassigning a change in pixel value for at least one period, to adesignated period.

FIG. 6 shows an example of color scheme in the color scale shown in (C)of FIG. 5.

The three orthogonal axes in FIG. 6 represent R values, G values and Bvalues, respectively. Similarly to FIG. 4, the R value, G value and Bvalue corresponding to each time phase within a designated period can bedetermined along the sides of the color triangle. Specifically, thecolors can be arranged so that the G value and the B value become zeroand the R value becomes the maximum value at the starting time phase T1,the R value and the B value become zero and the G value becomes themaximum value at the middle time phase between the starting time phaseT1 and the ending time phase T2, and the R value and the G value becomezero and the B value becomes the maximum value at the ending time phaseT2, similarly to an example shown in FIG. 4.

When the colors are arranged as shown in FIG. 6, a color scale in whicha color phase showing the maximum value changes among red, green andblue between the starting time phase T1 and the ending time phase T2 canbe generated. That is, a color scale whose color changes from red toblue through green within a designated period can be generated.

With regard to time phase other than a designated period, a pixel valuepattern different from a change in pixel value in the designated periodcan be assigned. For example, color phases may be changed between theinside and the outside of the designated period. As a more specificexample, a color scale can be generated so that the color phase changesfrom white to red at the time phases before the starting time phase T1while the color phase changes from blue to white at the time phasesafter the ending time phase T2.

Furthermore, a transmittance different from that in a designated periodcan also be assigned to time phase other than the designated period. Asa specific example, a color scale can be generated so that thetransmittance changes from the maximum value to zero at the time phasesbefore the starting time phase T1 while the transmittance changes fromzero to the maximum value at the time phases after the ending time phaseT2. That is, the transmittance may be changed in a predetermined range,in time phases outside the designated period. In this case, it is notnecessary to change color values, such as R value and B value, outsidethe designated period.

As described above, at least one of pixel values, including R value, Gvalue and B value, and the transmittance, in the time phase rangesoutside the designated period can be changed from those within thedesignated period.

Each color scale after the change as shown in (C) of FIG. 3 and (C) ofFIG. 5 can also be changed dynamically. Specifically, plural colorscales can be generated by changing at least one of a phase and a periodof change in pixel value of a color scale as shown in (C) of FIG. 3 or(C) of FIG. 5. Changing a phase of change in pixel value corresponds toshifting a color scale in the time phase direction. Meanwhile, changinga period of change in pixel value corresponds to expanding orcontracting a color scale in the time phase direction.

FIG. 7 shows an example of color scales generated for dynamicallychanging the color scale shown in (C) of FIG. 3, and FIG. 8 shows anexample of color scales generated for dynamically changing the colorscale shown in (C) of FIG. 5.

Each of (A) of FIG. 7 and (A) of FIG. 8 shows concentration profiles ofa contrast agent at two dimensional positions (xi, yj) (i=1, 2, 3, . . ., m; j=1, 2, 3, . . . , n) and arrival time phases Tmax(xi, yj) of thecontrast agent specified based on the maximum values MAXs of theconcentration profiles. Therefore, in each graph shown in (A) of FIG. 7and (A) of FIG. 8, the horizontal axis shows time phases and thevertical axis shows relative signal intensities corresponding toconcentrations of the contrast agent.

When a color scale, in which the change in pixel value for one period isassigned multiple times as shown in (C) of FIG. 3, is changeddynamically, what is necessary is to generate plural color scales byshifting the color scale shown in (C) of FIG. 3 in the change directionof the pixel value, as shown in (B) of FIG. 7. Similarly, when a colorscale, in which the change in the pixel value for one period is assignedto the designated period as shown in (C) of FIG. 5, is changeddynamically, what is necessary is to generate plural color scales byshifting the color scale shown in (C) of FIG. 5 in the change directionof the pixel value, as shown in (B) of FIG. 8.

When the color coding of parametric image data is performed using colorscales having different color schemes as described above, frames ofparametric image data corresponding to the color scales are generated.Thus, it becomes possible to display the frames of generated parametricimage data in the color scale direction as a moving image.

For example, in the example shown in (B) of FIG. 8, parametric imagedata can be generated, using the plural color scales, as a moving imagein which changes in pixel values different from each other have beenassigned to a period shorter than the period from the initial time tothe ending time of time changes in concentrations of a contrast agent.Furthermore, plural color scales may be generated by changing not only aphase of change in pixel value but also a period of the change in pixelvalue, as described above.

As described above, blood vessel image data can be generated as a movingimage according to plural color scales generated by changing at leastone of a phase and a period of change in pixel value for at least oneperiod. When parametric image data as blood vessel image data aredisplayed as a moving image, blood and a contrast agent can be displayedin color as if they flowed.

Note that, parametric image data can be generated, using the colorscales, as a moving image having a frame interval different from that ofX-ray contrast image data. That is, a frame interval for switching acolor scale to a different color scale can be set to a desirableinterval appropriate for a diagnosis, independently of the frameinterval of the X-ray contrast image data. Therefore, a moving speed ofthe colors which simulate blood flows can be set to a desired speed.

Therefore, it becomes possible to understand flows of a contrast agentand blood more easily. In particular, human eyes have high visibility tored. Therefore, generating a moving image in which red moves during afocused period from the starting time phase T1 to the ending time phaseT2 allows easy understanding of a blood flow dynamic state in a focusedregion.

As a specific example, when colors are changed in the designated periodas shown in (B) of FIG. 8, a color corresponding to each time phase canbe changed in time. In this case, a color changes among red, green andblue even at a same time phase. With regard to the outside of thedesignated period, colors at the starting time phase T1 and the endingtime phase T2 can be gradually changed into white respectively, or thetransmittances of colors can be changed.

Meanwhile, in the case of the color scale in which color values havebeen changed periodically as shown in (B) of FIG. 7, plural color scalescan be generated by gradually changing the initial color value in eachperiod, as mentioned above.

The color values including the R value, the G value and the B value canalso be changed into values other than the maximum values. Specifically,when parametric image data are generated by the above-mentioned colorscale, a brightness value at each pixel, at which a value of aconcentration profile of a contrast agent has not become zero bylow-pass filtering processing or the like, becomes the maximum value.That is, a brightness value at each pixel at which a contrast agentarrived becomes the maximum value, regardless of a concentration of thecontrast agent.

Thus, brightness values of parametric image data can be changed so thatconcentrations of a contrast agent can be understood. In other words,parametric image data having brightness values according toconcentrations of a contrast agent at a specific condition, such as themaximum values, can be generated as blood vessel image data.

Specifically, when the maximum R value, G value and B value before thechange in brightness values are R₀, G₀ and B₀, respectively, the Rvalue, G value and B value after the change in brightness values can bedetermined by multiplying each of the values R₀, G₀ and B₀ by acoefficient k, as shown in expression (1).

(R,G,B)=(kR ₀ ,kG ₀ ,kB ₀)  (1)

In expression (1), the coefficient k is set to a value not less thanzero and not more than one, corresponding to a concentration of acontrast agent. For example, the coefficient k can be determined byexpression (2).

k=P(x,y)/P ₀  (2)

wherein P(x, y) represents a value, corresponding to a specificcondition such as the maximum value, of a concentration profile of acontrast agent at a position (x, y), obtained as an image signal valueof X-ray contrast image data or DSA image data, and P₀ represents aconstant.

When the coefficient k is set by expression (2), the coefficient kbecomes a value proportional to the value P(x, y) of a concentrationprofile of a contrast agent. Therefore, the brightness values (R, G, B)of parametric image data can also be brightness values each proportionalto the value P(x, y) of a concentration profile of a contrast agent.Furthermore, brightness values at a pixel where a concentration of acontrast agent is a noise level and brightness values at a pixel wherenoises have actually occurred can be made small enough.

The constant P₀ can be set to the maximum value of the value P(x, y) ofa concentration profile of a contrast agent in spatial directions, or anarbitrary value which has been determined empirically. Note that, whenthe constant P₀ is set to a value smaller than the maximum value of thevalue P(x, y) of a concentration profile of a contrast agent, thecoefficient k may become a value larger than one, by the calculation ofexpression (2). In such a case, the coefficient k has only to be set toone.

Then, when a pixel value adjusted by expression (1) is assigned to eachpixel position (x, y), parametric image data in which blood vessels havebeen depicted in colors and brightness according to arrival time phasesand concentrations of a contrast agent can be generated. Note that, theadjustment of brightness values shown in expression (1) can be performedat the time of the color coding in the color coding part 23.

The parametric image data generated in the parametric image generationpart 21 as described above can be displayed on the display 14, similarlyto X-ray contrast image data or DSA image data. Furthermore, theparametric image data can be stored in the image memory 16 as necessary.

FIG. 9 shows an example of parametric image generated in the parametricimage generation part 21 shown in FIG. 1.

In a parametric image, blood vessels into which a contrast agent hasbeen injected are displayed in color while brightness values become zeroin regions without the contrast agent, as shown in FIG. 9. Furthermore,the blood vessels are depicted as a region or regions where colorschange according to arrival times of the contrast agent. Therefore, howblood and the contrast agent flow can be observed by colors.

In the X-ray diagnostic apparatus 1 and the medical image processingapparatus 12 having the functions and configurations as described above,the imaging system 2 and the control system 3 cooperating with eachother function as an image acquisition system configured to acquire atleast X-ray contrast image data from the object O. Furthermore, the timephase specifying part 22 and the color coding part 23, cooperating witheach other, of the parametric image generation part 21 function as ablood vessel image generation part configured to obtain time changes inconcentrations of a contrast agent based on at least X-ray contrastimage data, and generate blood vessel image data, having pixel valuescorresponding to times at which the concentrations of the contrast agentbecome a specific condition, according to a color scale. In addition,the color scale adjustment part 24 of the parametric image generationpart 21 functions as a pixel value scale generation part configured togenerate a color scale by assigning a change in pixel value for at leastone period, to a period shorter than the period from the initial time tothe ending time of the time changes in the concentrations of thecontrast agent.

Note that, the X-ray diagnostic apparatus 1 and the medical imageprocessing apparatus 12 may be configured by other elements so long assimilar functions as the image acquisition system, the blood vesselimage generation part and the pixel value scale generation part areprovided in the X-ray diagnostic apparatus 1 and the medical imageprocessing apparatus 12. For example, the medical image processingapparatus 12 may be configured by installing a medical image processingprogram, which makes a computer function as the blood vessel imagegeneration part and the pixel value scale generation part, to thecomputer. In that case, the medical image processing program can berecorded in an information recording medium to be distributed as aprogram product so that a general purpose computer can be used as themedical image processing apparatus 12.

Next, an operation and an action of the X-ray diagnostic apparatus 1 andthe medical image processing apparatus 12 will be described.

FIG. 10 is a flow chart which shows an operation of the X-ray diagnosticapparatus 1 shown in FIG. 1 and processing in the medical imageprocessing apparatus 12 shown in FIG. 1.

First, in step S1, X-ray image data are acquired without a contrastagent. Specifically, the imaging system 2 moves to a predeterminedposition and an X-ray is exposed from the X-ray tube 6 towards an objectO set on the bed 10, under control by the control system 3. Then, theX-ray which has transmitted the object O is acquired as X-ray projectiondata by the X-ray detector 7. The X-ray projection data acquired by theX-ray detector 7 are output as X-ray image data to the medical imageprocessing apparatus 12 through the A/D converter 11.

The X-ray image data may be acquired for one frame or multiple frames.When multiple frames of the X-ray image data are acquired and theaddition average of the multiple frames of the X-ray image data iscalculated in the filtering part 18, one frame of non-contrast X-rayimage data whose noises have been reduced can be generated.Subsequently, the non-contrast X-ray image data acquired as mentionedabove are stored in the image memory 16.

Next, in step S2, X-ray contrast image data are acquired continuously.For that purpose, the contrast agent injector 15 operates under acontrol by the control system 3, and a contrast agent is injected intothe object O. Subsequently, after a preset time has passed from thestart time of the contrast agent injection, the acquisition of the X-raycontrast image data starts. Then, the acquisition of the X-ray contrastimage data is performed continuously in a predetermined period. Thereby,the time series X-ray contrast image data are stored sequentially in theimage memory 16. The flow of acquiring the X-ray contrast image data issimilar to the flow of acquiring non-contrast X-ray image data.

Next, in step S3, the DSA image data are generated by the subtractionpart 17. More specifically, the time series DSA image data are generatedsequentially by subtraction processing of the time series X-ray contrastimage data using the non-contrast X-ray image data as mask image data.The generated time series DSA image data are stored sequentially in theimage memory 16.

The time series X-ray contrast images or the time series DSA images canbe displayed as live images in real time on the display 14. Furthermore,the time series X-ray contrast images or the time series DSA images canbe also displayed on the display 14 after the X-ray imaging. When theDSA images are displayed afterward, the DSA image data can be generatedby performing subtraction processing for only a time phase perioddesignated by an operation of the console 5.

Next, in step S4, time changes in concentrations of the contrast agentare generated by the time phase specifying part 22. Specifically, thetime series X-ray contrast image data or the time series DSA image datain a time phase period designated by operations of the console 5 aretaken into the time phase specifying part 22. Then, a concentrationprofile showing a time change in concentration of the contrast agent asshown in (A) of FIG. 3 or (A) of FIG. 5 is generated for every pixelposition in the time phase specifying part 22.

Note that, the filtering part 18 can perform one or both of low-passfiltering processing and running average processing in one or both ofspatial directions and the time direction, as preprocessing orpostprocessing of the generation of the concentration profiles of thecontrast agent. Thereby, smooth concentration profiles, of the contrastagent, having less noises can be generated. In addition, concentrationprofiles of the contrast agent whose data intervals are shorter thansampling intervals can also be generated by interpolation processing,gravity center calculation, or curve fitting in the time phasespecifying part 22.

Next, in step S5, arrival time phases of the contrast agent at therespective pixel positions are identified, by the time phase specifyingpart 22, based on the concentration profiles of the contrast agent.Specifically, the arrival time phase of the contrast agent can beidentified for every pixel position by data processing, such as peakdetection processing or threshold value processing, of the concentrationprofiles of the contrast agent.

Note that, after the time phases have been specified by the dataprocessing such as peak detection processing or threshold valueprocessing, continuous concentration profiles only in periods close tothe specified time phases may be calculated by interpolation processing,gravity center calculation, or curve fitting. In that case, the truearrival time phases of the contrast agent are detected by dataprocessing, such as peak detection processing or threshold valueprocessing, of the acquired continuous concentration profiles, for thesecond time.

Next, in step S6, the color scale adjustment part 24 generates a colorscale for color coding of a two dimensional map of the arrival timephases of the contrast agent acquired by the time phase specifying part22. The color scale adjustment part 24 can generate not only a generalcolor scale whose color phase changes continuously from the initial timephase to the last time phase at a constant rate of change as shown in(B) of FIG. 3 or (B) of FIG. 5 but also a color scale as shown in (C) ofFIG. 3 or (C) of FIG. 5 by increasing a change rate in color phase of anormal color scale.

In a case of generating a color scale whose color phase changescontinuously and periodically as shown in (C) of FIG. 3, the color scalecan be generated by specifying the period Tscale, in which the colorphase changes, and changing the color phase in each period Tscale, by anoperation of the console 5. Alternatively, these necessary conditionsmay be previously set as default values. A color phase at the startingtime phase in each period Tscale can be designated arbitrarily.Furthermore, when a color phase at the initial time phase ofconcentration changes of a contrast agent is not set to a color phase atthe starting time phase in each period Tscale, the color phase at theinitial time phase needs to be designated.

Meanwhile, in a case of generating a color scale having a continuouscolor phase change, within a designated time phase period, differentfrom that outside the designated time phase period, as shown in (C) ofFIG. 5, the color scale can be generated by designating the startingtime phase T1 and the ending time phase T2 of the time phase period, towhich the continuous color phase change is assigned, by operation of theconsole 5. The starting time phase T1 and the ending time phase T2 canbe designated by selecting an image from the time series X-ray contrastimages or the time series DSA images displayed on the display 14 byoperation of the console 5.

Next, in step S7, the color coding part 23 performs color coding, of thetwo dimensional map of the arrival time phases of the contrast agent,based on the color scale generated by the color scale adjustment part24. Specifically, an R value, a G value, and a B value corresponding toan arrival time phase of the contrast agent are assigned to each pixel,as pixel values, according to the color scale. Thereby, parametric imagedata are generated.

At this time, it is desirable to multiply each of the R value, the Gvalue and the B value by a coefficient corresponding to a concentrationof the contrast agent at the arrival time phase of the contrast agent.Thereby, parametric image data can be generated so that a brightnessvalue at a pixel, at which a concentration of the contrast agent at thearrival time phase of the contrast agent is relatively high, isrelatively high while a brightness value at a pixel, at which aconcentration of the contrast agent at the arrival time phase of thecontrast agent is relatively low, is relatively low.

Then, the parametric image generated as described above can be displayedon the display 14. The parametric image can also be displayed as amoving image by shifting, and/or expanding or contracting the colorscale in the time phase direction. Consequently, observing theparametric image allows a user to recognize blood vessels into which acontrast agent flows. In particular, a color phase change in the colorscale has been assigned to a short time phase period, and therefore,blood vessels in which arrival time phases of a contrast agent are nearto each other can be easily distinguished by a difference in color.

That is, the X-ray diagnostic apparatus 1 and the medical imageprocessing apparatus 12 as described above are configured to generateblood flow image data in color by color coding of specific time phases,such as arrival time phases, of a contrast agent with a color scaleaccording to time phases and contract a continuous color phase change ofthe color scale in the time phase direction in order to improve timephase identification ability by color.

Therefore, according to the X-ray diagnostic apparatus 1 and the medicalimage processing apparatus 12, adjacent blood vessels can be easilydistinguished as a difference in color phase even when a difference ininflow time phase, arrival time phase or outflow time phase of acontrast agent is small among the blood vessels.

In particular, it is important to observe a blood flow into a diseasepart between arteries and veins, in a diagnosis of a cerebralarteriovenous malformation or a dural arteriovenous fistula. Therefore,it is necessary to distinguish blood vessels into which a contrast agentflows. However, DSA images are displayed with a gray scale, andtherefore, distinguishing contrast-enhanced blood vessels is difficult.

In contrast, the X-ray diagnostic apparatus 1 and the medical imageprocessing apparatus 12 are configured to be able to set a period of acolor phase change in a color scale to be short, according to a timephase difference which should be identified. Accordingly, colors changefor every blood vessel even when a contrast agent flows into focusedblood vessels almost simultaneously. Therefore, the blood vessels can beeasily distinguished.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

For example, an example case of generating blood vessel image data ascolor parametric image data, using a color scale, has been described inthe embodiment described above. Alternatively, blood vessel image datamay also be generated using a gray scale. Specifically, blood vesselimage data having pixel values corresponding to times whenconcentrations of a contrast agent become a specific condition can begenerated according to a gray scale or a color scale. Furthermore, agray scale or a color scale can be generated by assigning a change inpixel value to a period shorter than the period from the initial time tothe ending time of time changes in concentrations of a contrast agent.

When blood flow image data are generated using a gray scale, acontinuous change in brightness value instead of a color phase change isto be assigned, as a change in pixel value, to a period shorter than theperiod from the initial time to the ending time of time changes inconcentrations of a contrast agent. In that case, each brightness valuecan also be set to a value according to a concentration of the contrastagent by multiplying the brightness value by a coefficient k accordingto the concentration of the contrast agent.

Similarly, when blood flow image data are generated using a color scale,not only a continuous color phase change but a continuous change inbrightness value can also be assigned as a change in pixel value asdescribed above. In that case, each brightness value can also be set toa value according to a concentration of a contrast agent by multiplyingthe brightness value by a coefficient k according to the concentrationof the contrast agent.

As described above, a change in pixel value assigned to a period shorterthan the period from the initial time to the ending time of time changesin concentrations of a contrast agent may be a continuous color phasechange, a continuous change in color brightness value, or a continuouschange in gray brightness value.

In addition, the X-ray diagnostic apparatus 1 of which the X-ray tube 6and the X-ray detector 7 have been fixed to the both ends of theC-shaped arm 8 has been exemplified in the embodiment described above.Similarly, an X-ray diagnostic apparatus having another structure canalso generate parametric image data. Examples of an X-ray diagnosticapparatus having another structure include an X-ray diagnostic apparatusof which each of the X-ray tube 6 and the X-ray detector 7 is fixed toan independent arm, besides an X-ray diagnostic apparatus havingmultiple arms or an X-ray diagnostic apparatus including movementstructures for moving arbitrary arms along axes in arbitrary directions,such as an arc axis or a straight axis. When each of the X-ray tube 6and the X-ray detector 7 is fixed to an independent arm, it is practicalto install driving structures, such as an expansion and contractionstructure, a rotating structure, a joint structure and a link mechanism,on each of the first arm holding the X-ray tube 6 and the second armholding the X-ray detector 7.

Further, an example case of generating parametric image data, which areblood vessel image data having pixel values corresponding to times atwhich concentrations of a contrast agent become a specific condition,based on X-ray contrast image data acquired by the X-ray diagnosticapparatus 1 has been described in the embodiment described above.However, parametric image data may also be generated based on bloodvessel image data acquired by another image diagnostic apparatus(modality).

For example, in a case of using an MRI (magnetic resonance imaging)apparatus, MRA (magnetic resonance angiography) image data ornon-contrast MRA image data can be acquired as contrast imaging ornon-contrast imaging. In a case of acquiring contrast MRA image data,blood flow dynamic state information can be obtained as time changes inconcentrations of a contrast agent. Meanwhile, in a case of acquiringnon-contrast MRA image data, blood flow dynamic state information can beobtained as changes in image values enhanced by applying a spin labelingpulse, such as an ASL (arterial spin labeling) pulse, or an imagingmethod, such as a TOF (time of flight) method.

On the other hand, in a case of acquiring 4D (four dimensional) X-ray CT(computed tomography) contrast image data using an X-ray CT apparatus,blood flow dynamic state information can be obtained as time changes inconcentrations of a contrast agent. Alternatively, an ultrasoniccontrast scan using an ultrasonic diagnostic apparatus can also obtainblood flow dynamic state information as time changes in concentrationsof a contrast agent.

Whether contrast blood vessel image data have been acquired by an imagediagnostic apparatus or non-contrast blood vessel image data have beenacquired, blood flows can be observed as time changes in pixel valuescorresponding to blood vessels.

Therefore, in a case of generating parametric image data based on bloodvessel image data acquired by an arbitrary image diagnostic apparatus, amedical image processing apparatus has a blood vessel image generationpart which is configured to obtain time changes in pixel valuescorresponding to blood vessels, based on the blood vessel image dataacquired by the image diagnostic apparatus, and generate blood vesselimage data, having pixel values corresponding to times at which thepixel values corresponding to the blood vessels become a specificcondition, according to a gray scale or a color scale. Furthermore, themedical image processing apparatus has a pixel value scale generationpart which is configured to generate the gray scale or the color scale,by assigning a change in pixel value for at least one period, to aperiod shorter than the period from the initial time to the ending timeof the time changes in the pixel values corresponding to the bloodvessels.

What is claimed is:
 1. A medical image processing apparatus comprising:processing circuitry configured to obtain time changes of concentrationsof a contrast agent, based on at least X-ray contrast image data;generate a gray scale or a color scale by assigning a change in pixelvalue for at least one period, to a period shorter than a period from aninitial time to an ending time of the time changes of the concentrationsof the contrast agent; and generate blood vessel image data according tothe gray scale or the color scale, the blood vessel image data havingpixel values corresponding to times at which the concentrations of thecontrast agent become a specific condition.
 2. A medical imageprocessing apparatus of claim 1, wherein the processing circuitry isconfigured to generate the gray scale or the color scale by assigning achange in pixel value, longer than the change in the pixel value for theone period, to the period from the initial time to the ending time ofthe time changes of the concentrations of the contrast agent.
 3. Amedical image processing apparatus of claim 1, wherein the processingcircuitry is configured to generate the gray scale or the color scale byassigning the change in the pixel value for the one period multipletimes, to the period from the initial time to the ending time of thetime changes of the concentrations of the contrast agent.
 4. A medicalimage processing apparatus of claim 1, wherein the processing circuitryis configured to generate plural gray scales or plural color scales byshifting the gray scale or the color scale in a direction of the changein the pixel value.
 5. A medical image processing apparatus of claim 1,wherein the processing circuitry is configured to generate plural grayscales or plural color scales by changing at least one of a phase and aperiod of the change in the pixel value for the at least one period, andgenerate the blood vessel image data as a moving image, according to thegray scales or the color scales.
 6. A medical image processing apparatusof claim 4, wherein the processing circuitry is configured to generatethe blood vessel image data using the gray scales or the color scales,the blood vessel image data being generated as a moving image in whichchanges of pixel values different from each other are assigned to theperiod shorter than the period from the initial time to the ending timeof the time changes of the concentrations of the contrast agent.
 7. Amedical image processing apparatus of claim 4, wherein the processingcircuitry is configured to generate the blood vessel image data usingthe gray scales or the color scales, the blood vessel image data beinggenerated as a moving image of which a frame interval is different froma frame interval of the X-ray contrast image data.
 8. A medical imageprocessing apparatus of claim 1, wherein the processing circuitry isconfigured to generate the gray scale or the color scale by assigningthe change in the pixel value for the at least one period, to adesignated period.
 9. A medical image processing apparatus of claim 3,wherein the processing circuitry is configured to generate a gray scaleor a color scale in which the change of the pixel value for the oneperiod, having a designated initial pixel value, is repeated in adesignated period.
 10. A medical image processing apparatus of claim 1,wherein the processing circuitry is configured to generate blood vesselimage data, having brightness values according to concentrations of thecontrast agent at the specific condition.
 11. A medical image processingapparatus of claim 1, wherein the specific condition is maximum values,a predetermined ratio of the maximum values, or a threshold value.
 12. Amedical image processing apparatus of claim 1, wherein the processingcircuitry is configured to generate the blood vessel image data based ontime changes, of the concentrations of the contrast agent, having a datainterval shorter than a sampling interval of the concentrations of thecontrast agent.
 13. A medical image processing apparatus of claim 12,wherein the processing circuitry is configured to obtain the timechanges, of the concentrations of the contrast agent, having the datainterval shorter than the sampling interval of the concentrations of thecontrast agent, by interpolation processing, curve fitting processing,or gravity center calculation processing.
 14. A medical image processingapparatus of claim 1, wherein the processing circuitry is configured togenerate the blood vessel image data based on time changes, of theconcentrations of the contrast agent, after running average processingin at least one of a time direction and spatial directions.
 15. Amedical image processing apparatus of claim 1, wherein the processingcircuitry is configured to generate the blood vessel image data based ontime changes, of the concentrations of the contrast agent, afterlow-pass filtering processing in at least one of a time direction andspatial directions.
 16. A medical image processing apparatus of claim 8,wherein the processing circuitry is configured to generate the grayscale or the color scale by assigning a pixel value, different from thechange in the pixel value, to a period other than the designated period.17. A medical image processing apparatus of claim 8, wherein theprocessing circuitry is configured to generate the gray scale or thecolor scale by assigning a transmittance, different from a transmittancein the designated period, to a period other than the designated period.18. A medical image processing apparatus of claim 1, wherein theprocessing circuitry is configured to generate the gray scale or thecolor scale by assigning a continuous change in color phase, acontinuous change in at least one color brightness value or a continuouschange in gray brightness value, as the change in the pixel value.
 19. Amedical image processing apparatus comprising: processing circuitryconfigured to obtain time changes in pixel value corresponding to ablood vessel, based on blood vessel image data acquired by an imagediagnostic apparatus; generate a gray scale or a color scale byassigning a change in pixel value for at least one period, to a periodshorter than a period from an initial time to an ending time of the timechanges in the pixel value corresponding to the blood vessel; andgenerate blood vessel image data according to the gray scale or thecolor scale, the blood vessel image data having pixel valuescorresponding to times at which pixel values corresponding to the bloodvessel become a specific condition.
 20. An X-ray diagnostic apparatuscomprising: an X-ray tube and an X-ray detector for acquiring at leastX-ray contrast image data from an object; and processing circuitryconfigured to obtain time changes of concentrations of a contrast agent,based on the at least X-ray contrast image data; generate a gray scaleor a color scale by assigning a change in pixel value for at least oneperiod, to a period shorter than a period from an initial time to anending time of the time changes of the concentrations of the contrastagent; and generate blood vessel image data according to the gray scaleor the color scale, the blood vessel image data having pixel valuescorresponding to times at which the concentrations of the contrast agentbecome a specific condition.
 21. A medical image processing methodcomprising: obtaining time changes of concentrations of a contrastagent, based on at least X-ray contrast image data; generating a grayscale or a color scale by assigning a change in pixel value for at leastone period, to a period shorter than a period from an initial time to anending time of the time changes of the concentrations of the contrastagent; and generating blood vessel image data according to the grayscale or the color scale, the blood vessel image data having pixelvalues corresponding to times at which the concentrations of thecontrast agent become a specific condition.
 22. An X-ray diagnosticmethod comprising: acquiring at least X-ray contrast image data from anobject; obtaining time changes of concentrations of a contrast agent,based on the at least X-ray contrast image data; generating a gray scaleor a color scale by assigning a change in pixel value for at least oneperiod, to a period shorter than a period from an initial time to anending time of the time changes of the concentrations of the contrastagent; and generating blood vessel image data according to the grayscale or the color scale, the blood vessel image data having pixelvalues corresponding to times at which the concentrations of thecontrast agent become a specific condition.